The present invention relates to a vehicle sensor, and more particularly to a sensor attachment arrangement for vehicle fluid directing component which provide an enhanced retention force over time.
Various types of air induction components such as air induction manifolds, air filter assemblies and throttle bodies are used in the field of internal combustion engines. Many known air induction components are presently manufactured of a non-metallic material such as nylon to simplify fabrication and reduce weight.
The prevalence of substantially non-metallic air induction components can create difficulties for the installation of sensors such as temperature sensors, manifold absolute pressure (MAP) sensors, mass air flow sensors, potentiometers and the like. Such sensors are commonly threaded directly into apertures in the air induction components. Other sensors include extended tabs which receive threaded fastener that enter the air induction components. During use over time, however, the air induction component heats up and the threaded sensor or fastener may tend to move away from its installed position. The sensor may then shift away from its original position and cause a degradation of performance.
Another known sensor attachment arrangement includes a barb which snaps onto a ledge. However, the known barb and ledge is relatively easy to disengage. A measure of a snap fit is the locking ratio which can be defined as the force to put the snap-fit in, divided by the force to take the snap fit object out. The locking ratio for the known barb arrangement is approximately 1:2. That is, it only requires approximately twice as much force to remove the barb as to insert it. A low locking retention ratio is particularly disadvantageous when located adjacent a high-vibration vehicle component.
Known sensor attachment arrangements are also typically unique for each particular sensor. The unique attachment arrangements complicate manufacture of the air induction component and increases the difficulties of substituting sensors for different vehicle and engine types.
Other known uses include provisions for creep in the attachment arrangement of toys. Typically, a barb and ledge or bayonet arrangement are provided on plastic toys which increase in retention force over time. However, the known toy attachment arrangements types are still relatively easy to disengage because of the simplified engagement arrangement.
Accordingly, it is desirable to provide a sensor assembly which can be easily, securely and inexpensively attached to a non-metallic fluid directing component and which provides an enhanced retention force as residual stresses formed during insertion are relieved. It is further desirable to provide a generic attachment arrangement to simplify manufacture of the air induction component and allow the interchangeability of sensors.
The present invention provides a vehicle sensor assembly of a relatively low density material for a vehicle fluid directing component such as an air intake manifold having a sensor receipt member formed of a relatively high density material. The sensor assembly includes a sensor engagement surface such as groove in a locating segment of the sensor. The sensor engagement surface defines an outer periphery dimension and a sensor receipt member engagement surface defines an inner periphery dimension which is of a smaller diameter than the free state outer diameter of the sensor engagement surface. Because the sensor engagement surface is larger than the sensor receipt member engagement surface, an interference fit is preferably established when the sensor is inserted into the sensor receipt member.
When the sensor is inserted into the sensor receipt member, the relatively softer sensor engagement surface is displaced from its free state by the relatively harder sensor receipt member engagement surface. A high stress area is thereby formed in the sensor adjacent the sensor engagement surface. As the sensor is inserted into the sensor receipt member in a particular direction the high stress area will substantially form on the side of the sensor engagement surface opposite the direction of insertion. The relatively softer sensor engagement surface is resilient and will always attempt to return to its free state position to relieve the high stress area. In attempting to return to its free state, the sensor engagement surface will xe2x80x9ccreepxe2x80x9d toward a low stress area.
Over a period of time, the xe2x80x9ccreepxe2x80x9d from high stress area to the low stress area will tend to displace the sensor engagement surface relative to the sensor receipt member engagement surface. This movement will increase in rate if the sensor engagement surface is exposed to heat. Accordingly, the sensor body material will respond by xe2x80x9ccreepingxe2x80x9d toward the vehicle fluid directing component. The present invention thereby takes advantage of the relief of residual stresses formed during insertion of the sensor body to tighten the mounting of the sensor into the vehicle fluid directing component.